Finding wolf homesites: improving the efficacy of howl surveys to study wolves

Locating wolf (Canis lupus) homesites is valuable for understanding the foraging behavior, population dynamics, and reproductive ecology of wolves during summer. During this period wolf pack members (adults and pups) readily respond to simulated wolf howls (i.e., howl surveys), which allows researchers to estimate the location of the homesite via triangulation. Confirming the actual locations of homesites via ground truthing is labor intensive because of the error surrounding estimated locations. Our objectives were (1) to quantify observer error during howl surveys and compare amongst experience levels, (2) provide a simple method for locating homesites in the field by incorporating observer error, and (3) further document the value of this method for monitoring wolf packs throughout the summer. We located 17 homesites by howl surveys during 2015-2017 in the Greater Voyageurs Ecosystem, Minnesota, USA. Of 62 bearings taken by observers during howl surveys, bearings erred by an average of 7.6° ± 6.3° (SD). There was no difference in observer error between novice and experienced observers. A simple way to increase efficiency when searching for homesites is to search concentric areas (bands) based on estimated observer error, specifically by: (1) adding ±10° error bands around howl survey bearings when ≥3 bearings can be obtained, (2) ±10° and ±20° error bands when 2 bearings are obtained, and (3) ±10° and ±26° error bands when 1 bearing is obtained. By incorporating observer error and understanding how frequently and how far wolves move homesites, it is possible to monitor wolf packs and confirm most, if not all, homesites used by a pack from at least June until August without having a collared individual in a pack.